It is desirable to monitor internal bodily events, sometimes over a period of time, without immediate access to medical facilities. For example, the ability to track medicine ingestion and absorption into the body is useful for verifying proper usage, monitoring drug interactions, controlling dosage and maintaining inventory control.
Traditional methods of obtaining internal physiological information include: physically probing the body via an orifice or incision with tools such as endoscopes or laparoscopes; imaging the body with modalities such as x-ray, computed tomography or magnetic resonance imaging; or collecting biological samples such as blood, saliva, bodily secretions, or biopsy tissue. It would be appealing to probe the living body without the effort, expense, inconvenience and risk of injury or infection involved with the above methods.
An improvement on these traditional means is the use of ingestible cameras, such as the Pillcam™ produced by Given Imaging (see www.pillcam.com). These swallowable cameras in pill format collect images and basic physical measurements such as pH and temperature as they travel through the digestive tract. Pillcam's™ main use is to collect internal images to help with diagnosis of conditions inside the digestive tract. These devices have been proven to provide useful information about the state of a subject without additional invasive medical procedures. However, such cameras are relatively complex, expensive, unpleasant to swallow, and are limited in their ability to collect physiological information.
Radio frequency identification (RFID) tags are a class of device that can also be applied to the problem of tracking internal physiological activities. An RFID tag includes an antenna made of a material that can be caused to sympathetically resonate by a field attuned to a particular frequency (typically in the radio range). The resonance of the antenna in the field in turn becomes a source of information by broadcasting at the resonant frequency. These devices are more flexible in their range of applications, less expensive, simpler and therefore more robust than the solutions discussed above. As shown in FIG. 1, the standard components of an RFID tag 10 include a circuit 12, a resonant cavity 14, and an antenna 16 assembled on a substrate 18 or other means of providing support to the components just stated. Current RFID technology offers many solutions that take advantage of a remote querying capability combined with decreasing cost.
RFID tags have a long history. During World War II the British used RFID tags to remotely distinguish between friendly and hostile approaching aircraft. The World War II VT Fuze manufactured by the Eastman Kodak Company and others emitted a radio signal that responded to the proximity of a metal target by becoming increasingly in phase until the combined strength of the emitted and reflected signals was sufficient to activate the fuze.
Further evolution of the RFID tag occurred when Thermin pioneered the use of passive RF to spy upon the American Embassy in Moscow. The precursor to modern passive RFID tags, an external radio transmission provided power to a resonant circuit at certain frequencies. Certain conditions, such as people speaking in a room, would modify the modulation of the resonance, which would then be received and demodulated, creating an extremely simple and robust wireless means for listening to remote conversations.
More recently, RFID technology has been applied to the medical field in inventions such as affixing RFID tags 10, to containers for medicine 20, shown in FIG. 1, patients, and medicine dispensers, such as IV bottles. These RFID tags can be remotely queried in order to track the medicine usage. (See U.S. Patent Application Publication Nos. 2005/0088306 A1 (Andreasson et al.) and 2004/0008123 A1 (Carrender et al.). One major shortcoming of this approach is that the RFID tag is on the container and not in the medicine that is ingested. Although usage can be tracked, a method that verifies ingestion and digestion of medicine by a specific person cannot be implemented.
Although potentially useful, another approach is to provide RFID tags that can be implanted in a living body without fear of breakdown or interaction. U.S. Patent Application Publication No. 2003/0058110 A1 (Rich) refers to an RFID system that can be embedded under the patient's skin. However, RFID tags that require implantation in the human body for monitoring biological activity and medicine delivery will also require removal when no longer needed, a near certainty for most conditions needing medicinal treatment. Permanently implanted devices and tags require engineering and construction to attempt to preclude damage and failure as is taught in U.S. Pat. Nos. 6,083,523, 5,874,099 (both to Dionne et al.), and others by Dionne et al. and may be cost prohibitive for the majority of the patient population. Simple systems of permanent RFID tags embedded under the skin have been developed for tracking and identifying pets such as disclosed in U.S. Pat. No. 5,850,196 (Mowers)
Finally, in cases where the RFID tag is meant to pass through the body, as the Pillcam™ does, engineering is required to ensure that the RFID tag circuit is not damaged in the process of ingestion and elimination, again potentially increasing the cost and size of the device.
Therefore a need exists for a system to accurately monitor a patient's ingestion and digestion of medicine, without the use of permanently embedded equipment or cost prohibitive RFID solutions.